The present invention is directed to a method and device for removing particulates from vapor streams. More particularly, but not exclusively, it is directed to removing carbonaceous particles from vapor or gas streams using a self-cleaning filter.
The levels of particulate matter in the air is a matter of growing concern. A major source of particulate matter pollution are the exhaust gasses from power plants, manufacturing operations, and internal combustion engines. Accordingly, removal of particulates from these and other vapor streams prior to the vapor stream reaching the atmosphere is an important step in controlling particulate matter pollution.
Typically, removal of particulate matter from vapor streams is performed with electrostatic precipitators or particulate traps. In each of these methods, a vapor stream is passed through a device where particulate matter from the vapor stream is physically collected in the precipitator or trap. In most cases, the collected matter accumulates on the precipitator or trap, eventually clogging or otherwise reducing the efficiency of the device. Thus, periodically, the precipitator or trap must be emptied of collected material or the filter replaced. This process can be time consuming and expensive since the device must ordinarily be taken off line and at least partially disassembled and/or reconditioned before being placed back in operation. Disposal of the collected material or spent filter introduces further difficulties and waste.
In some cases, attempts have been made to clean precipitators or traps automatically and without requiring that they be taken off-line. For example, the temperature in the device around the collected particles can be elevated to a point that collected particles combust. However, numerous design and implementation difficulties exist in constructing devices that can achieve and withstand the stressful conditions of elevated temperatures and/or extended operating temperature ranges. Moreover, elevated temperatures can, in certain cases, adversely influence the chemistry of particle combustion, limit the choice of available materials, or otherwise reduce the overall efficiency of collection and disposal of particulates.
A need exists for improved systems and techniques that can efficiently remove particulates from vapor streams for longer periods before requiring attention. A need also exists for improved systems and techniques that can remove particulates and dispose of the removed particulates in an efficient and cost effective manner. A need also exists for a particulate filter that can be regenerated without requiring substantially elevated temperatures and/or needing to be taken off line. One or more of these or other needs are met by one or more embodiments of the present invention.
In one embodiment there is provided a novel technique for removing particulates from a vapor stream. In one refinement, the technique includes depositing particulates onto filter material and then vaporizing the collected particulates using a nonthermal plasma. Where the filter includes dielectric material, the dielectric is polarized by application of a first potential across a pair of electrodes around the filter to electrically collect particulates from the vapor stream. The nonthermal plasma is then formed by periodically applying a second higher potential across the pair of electrodes to vaporize the collected particulates. In further refinements the nonthermal plasma is automatically formed in response to deposition of a predetermined quantity of particulates, where the predetermined quantity is determined by monitoring the pressure drop across the filter. In a still further refinement, the filter material includes a catalyst active under nonthermal plasma conditions to assist vaporization of collected particulates at reduced power consumption.
There is also disclosed a novel vapor filtration device comprising a first electrode, a second electrode, and a filter between the first and second electrodes. The filter can be formed of dielectric material and the device operated by applying a first electric potential between the electrodes to polarize the dielectric material such that upon passing a vapor stream through the filter, particles from the vapor stream are deposited onto the filter. After depositing the particles a second higher voltage can then be applied between the electrodes to form a nonthermal plasma around the filter to vaporize the collected particles thereby cleaning the filter. In particular refinements, the filter is packed a bed or a serpentine filter mat.
In one advantageous aspect, the invention provides a technique where collected particulates can be vaporized without requiring elevated temperatures. In another aspect, a technique is provided where a nonthermal plasma vaporizes collected particulates to regenerate a particulate collection system without requiring the system to be taken off line. In still another aspect, an automated system for collecting and vaporizing particulates from a vapor stream to reduce pollution in a cost effective manner is provided. In yet a further aspect, a novel filtration system with a self cleaning filter is provided.